Such coupling networks are used, for example, in apparatus for checking the performance of several transmission lines with the aid of a processor to which pilot signals from these lines are successively fed. The coupling network is provided in that case with a plurality of inputs and a single output, the latter being tied to a common section of the several signal paths originating at the respective inputs. Conversely, a pilot signal may be fed in at a single input tied to a common section of several signal paths with terminate at respective outputs leading to lines that are to be successively tested.
For the selective transmission of pilot signals from or to any one of a plurality of stations located in a group on one side of the coupling network, the netowrk generally includes a plurality of connectors respectively linked with these stations. Activation of a selected connector, usually accompanied by other switching operations in other parts of the coupling network, establishes the desired signal path between the selected station of the group and the remote station. The other connectors, which are in an inactive state, cut off their respective stations to prevent signal leakages which could occur inside the network especially when the pilot signals are of high frequency. Thus, for example, where the lines to be tested serve for the transmission of telephone messages via high-frequency carriers, such leakages may result in undesirable cross-talk. In other instances, leakage may lead to contamination of the pilot signal being processed and may thus give rise to an incorrect evaluation.
To insure an effective cutoff it is known to provide each connector with a set of switches of the mechanical or the electronic type which are alternately in shunt and in series with the signal path, the shunt switches being closed and the series switches being open in the inactive state of the connector whereas the reverse relationship exists in its active state. A malfunction of any such switch, such as a "sticking" of a mechanical contact in an open or closed position, may seriously impair the decoupling effect of an inactive connector. Such malfunctions are liable to occur especially with automatic testing equipment in which these switches are subject to frequent reversals.